I've been trying to think of a method for fading a particle in and out of scene gradully i.e. without using a toggle. The specific example I'm thinking of is P_Water_Mist2.

I initially thougtht there would be some controls in like Vector Material Parameters which you can poll in Matinaee. But all I found was float Particle Paraemter. I'm not sure how to access these paramenters but I don't think it would affect colour or alpha which is my current line of thinking.

I tried using the Set Particle Parameter in Kismet to change color to black but it seems to work more like a toggle, causing sharp changes and its not exactly the effect I'm after.

As I don't know cascade that well is there any way to expose the alpha channel to matinaee or create a fade sequence that I can poll inside of Kismet. Or any other way you know of that can be used. Alternatively are there any maps that create such an transition with particles?

Ok so I found a method that works. Perhaps not the way I original thought about it but as a work around its good enough.

I noticed that on toggling the particle off the sprite planes fade out but on toggling on they pop back very sharply. So that's half the equation. So after having no luck with the opacity settings - due to stupidity or ignorance I gave up and approached it from a different side. I tried shrinking the sprite in and out - which works in Matinee but not in game. So the alternative I found was just to move the particle in and out of scene. Setting the particles move properties to interpolating.

So toggle the sprite off then move the particle below scene. Then toggling on and slowly move the particle back into scene to transition it back. Not applicable for every application but in my case it works ok.